In smaller commercial establishments, it is often desirable to provide food warmers for the display of food whereby individual orders may be placed for specific items displayed. It has now become feasible to cook food items to order in such establishments utilizing infra-red energy.
Infra-red energy is particularly suited for smaller commercial establishments because the energy produced is directional and production does not require heated air currents which may be released into the ambient atmosphere as with convection ovens and the like. While microwave ovens are also useful in such establishments, microwave ovens have distinct disadvantages relative to the inability to brown bread or rolls and to char the exterior while cooking meat. Microwave ovens, however, are compact and suitable for countertop use.
In U.S. Pat. No. 4,960,977, assigned to the assignee of this invention, there was described a countertop-type infra-red radiation oven useful, for example, to cook pizza wherein the article to be cooked was disposed upon a mesh turntable. Infra-red emitters were disposed below and above the item to be cooked and on two of its four sides. Accordingly, as the turntable rotated, all sides of the food product were exposed to radiation for cooking.
In the case of pizza, the sides, bottom, and top all may have different cooking requirements. In the above-identified infra-red oven, the emitters were separately controlled. In addition, the top emitter was disposed in a movable shroud which could be adjusted in height over the turntable as desired. Shielding for the oven was not necessary because convection currents were not involved in the cooking process and only the directional radiation of the emitters used.
This type of oven was particularly suited to the use of etched foil emitters as contrasted to the use of conventional quartz tubes, nichrome wire and the like. The foil emitters use a relatively low wattage, have a rapid warm-up and cool-down, and can be adjusted to the desired medium range wavelength of cooking energy. In addition, a ceramic or other type shield is not necessary.
In certain infra-red emitters such as that described in U.S. Pat. No. 3,809,859, a refractory cover is provided over the wire heating elements, which cover then is the source of infra-red energy to the product to be cooked. This type of device then utilizes energy both to heat the refractory material and to then generate sufficient energy to direct the same onto the product to be cooked.
It is also known to provide conveyor ovens which utilize infra-red energy. Such devices are described, for example, in U.S. Pat. Nos. 4,245,613; 4,554,437; and 4,615,014. Such ovens are normally multi-zone type ovens and large type installations. In addition, as described in U.S. Pat. No. 4,363,955, conventional thinking used shortwave energy for food cooking such as infra-red energy in the wavelength of 1-2 microns as the preferred energy for cooking. In that latter identified patent, the conveyor oven utilized was intended to brown rolls previously partially cooked. To this end, infra-red radiating tubes were provided across the path of travel of a conveyor carrying the individual rolls with a plurality of tubes at the entrance emitting medium range microwaves, but the tubes interior to the conveyor or tunnel oven both above and below were short wavelength emitters.
As described in the above-identified patent, U.S. Pat. No. 4,960,977, it has been discovered that medium wavelength infra-red radiation is vastly desirable for cooking food as compared to the short range spectrum of 1.0 to 2.5 microns. In this way, the cooking can occur at wavelengths in excess of that absorbed by water of up to about, for example, 4.20 to 4.90 microns or higher.